Because booze dehydrates you, it can trick you into thinking you need food when your body is really calling for water.

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Photos:Reasons you're always hungry

When dehydration sets in, wires get crossed in the hypothalamus, leading you to grab a bag of chips when you really need a bottle of water.

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Photos:Reasons you're always hungry

Too little sleep can lead to surging levels of ghrelin, a hormone that stimulates appetite.

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Photos:Reasons you're always hungry

Stress reduces levels of the brain chemical serotonin, and that can make you feel hungry when you aren't.

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Photos:Reasons you're always hungry

Just looking at food\ cranks up levels of ghrelin, the hunger hormone

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Photos:Reasons you're always hungry

Antidepressants are known to affect appetite.

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Story highlights

Hunger is driven by diet, appetite hormones, and emotional factors, such as stress

Stress reduces levels of the brain chemical serotonin, and that can make you feel hungry when you aren't

Eating at a moderate pace prompts the release of hormones that tell your brain "no more"

(CNN)It's one thing to notice an uptick in appetite if you've been training hard at the gym, or if you're pregnant or PMS-ing. But when you always feel like a bottomless pit for no obvious reason, then something's definitely up. "Hunger is the physiological need for calories, water, and salt, and it's driven by a mix of factors, including your diet, appetite hormones, and emotional factors, such as stress," says Maggie Moon, RD, a Los Angeles-based nutritionist and owner of Everyday Healthy Eating. Figuring out why you can't stop shoveling it down is important, because excess hunger can tip you off to a physical or mental health issue—and giving in to that need to feed can send your BMI into dangerously unhealthy territory. These 11 things will help explain why your belly's been growling.

You're dehydrated

"Mild dehydration is often masked as feelings of hunger, when really your body just needs fluids," says Alissa Rumsey, RD, spokesperson for the American Academy of Nutrition and Dietetics. The confusion happens in the hypothalamus, the part of the brain that regulates both appetite and thirst. When dehydration sets in, wires get crossed in the hypothalamus, leading you to grab a bag of chips when you really need a bottle of water. "Prevent it by staying on top of your fluid intake, starting with a glass of water first thing in the morning," advises Rumsey. "If you feel hungry, and you haven't drank much that day, try drinking a glass of water and waiting 15 to 20 minutes to see if your hunger subsides."

You're a restless sleeper

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By the time you wake after a night of poor sleep, two hormones linked to appetite have already begun conspiring against you. "Too little sleep can lead to surging levels of ghrelin, a hormone that stimulates appetite, as well as decreased levels of leptin, a hormone that causes feelings of fullness," says Rumsey. Lack of shuteye on a regular basis makes you ravenous for another reason. After poor sleep, you're more likely to have serious fatigue and brain fog. Your system, desperate for a shot of energy, triggers cravings for sugar carbs, even if you're not actually hungry. Aim for 7 to 8 hours of sleep a night, and you'll get your energy level and hunger hormones back on track.

You load up on starchy carbs

Ever notice how one doughnut or cookie leaves you unable to resist eating another...until the whole box is just crumbs? That's your brain on starchy carbs. "Simple carbs, the kind found in sugary, white flour foods like pastries, crackers, and cookies, spike your blood sugar levels quickly, then leave them plunging soon after," says Moon. That blood sugar plunge causes intense hunger for more sugary carbs, and the cycle continues." Keep fluctuating blood sugar levels from sending you on a cravings roller coaster by avoiding simple-carb foods as much as possible. Get your carb fix with the complex, filling kind that contains lots of fiber. Almonds, apples, chia seeds, and pistachios are healthy options that ward off hunger pangs, suggests Moon.

You're a stress case

Who hasn't dealt with a high-pressure workday or relationship rough spot by giving into cravings for a pint of Rocky Road? But stress has a sneakier way of making you voracious. When you're tense, your system ramps up production of the stress hormones adrenaline and cortisol, says Rumsey. Elevated levels of these hormones trick your system into thinking it's under attack and needs energy, so your appetite starts raging. Stress also reduces levels of the brain chemical serotonin, and that can make you feel hungry when you aren't, says Moon. Consider it a case for making it to yoga class more often, or cranking up a soothing playlist on your commute home.

You drink too much alcohol

That pre-dinner cocktail or glass of wine meant to whet your appetite before dinner actually does just that, stimulating a feeling of hunger even if your stomach is full, says Moon. A small study published in the journal Appetite backs this up, finding that people were more likely to consume foods higher in calories after drinking alcohol. And because booze dehydrates you, it can trick you into thinking you need food when your body is really calling for water. Offset the effect by eating before you drink, and make sure to alternate your cocktails with water so you stay hydrated, says Rumsey.

You need to eat more protein

It sounds counterintuitive, but piling your plate with more food—lean protein and healthy fat, specifically—keeps hunger pangs at bay. "Not only does protein stay in your stomach and promote feelings of fullness, it's been shown to have an appetite-suppressing effect," says Rumsey. Aim for at least 46 grams of protein per day (best sources: Greek yogurt, eggs, lean meat, and whole grains), which is the RDA for women between 19 and 70. For men, it's 56 grams per day.

You aren't eating enough fat

Just like protein, unsaturated fat is also linked to feelings of satiety. "When you're satisfied after a meal, you are more likely to listen to your hunger cues and not eat again until you are truly hungry," says Rumsey. Add this heart-healthy, brain-boosting kind of fat to your meals in the form of oils, nuts and seeds, and avocados. Experts recommend that adults limit their fat intake to 20 to 35% of their total daily calories.

You skip meals

Yet another reason why ghosting on breakfast or forgoing other meals throughout the day backfires on you. When you skip a meal and your stomach is empty for too long, it produces an uptick in the hunger hormone ghrelin, which ramps your appetite, says Rumsey. "Ghrelin also prompts the GI tract to expect food to come. Your ghrelin levels are in overdrive, and so is your lust for food." When you finally give in, you're prone to a binge. As a general rule, try not to let more than 4 to 5 hours go by between meals. And even if you hate breakfast, eat something in the a.m. within an hour of waking, like yogurt, peanut butter and apple slices, or a soymilk smoothie.

You're bombarded by food porn

Pinterest recipe boards. Facebook photos of your friends' lunches. Late-night TV ads for takeout pizza. With images of food saturating our lives 24-7, it's no wonder so many of us are constantly craving the real thing. The connection between what we see and what we desire has been documented by science: a 2012 study from the journal Obesity found that just looking at food cranked up levels of ghrelin, the hunger hormone. Getting a whiff of food has a similar effect, says Moon. "Pleasant food aromas stimulate an involuntary physiological reaction: the mouth will salivate and the stomach will contract, mimicking hunger pangs," she says. Of course, you can't totally eliminate the possibility of seeing or smelling food. But try limiting your exposure, say by skipping TV commercials and un-following food brands on Instagram.

You inhale your food

When you wolf down your meal, your stomach might be full, but you haven't allowed your brain enough time to register that fullness. When your brain is still in the dark, it keeps your appetite high . . . and you continue eating. A study published in 2013 in the Journal of Clinical Endocrinology & Metabolism supports this, finding that eating at a moderate pace prompts the release of hormones that tell your brain "no more." Try eating your food slowly, savoring each bite and enjoying the ritual of a good meal. Then wait at least 20 minutes before deciding if you really do need another helping. That's about how long it takes for that fullness signal to reach your brain, says Rumsey.

You're on certain meds

The same drugs you might be taking regularly to treat a health condition can also drive you to raid the refrigerator. Antidepressants such as Zoloft and Paxil, as well as corticosteroids such as prednisone (prescribed to treat potentially dangerous flareups of the immune system due to allergies, asthma, inflammatory bowel disease like Crohn's disease, and some cancers), are known to affect appetite, says Rumsey. If you're on one of these prescription and feel hungry after a normal-sized meal, talk to your doctor to see if it's possible to switch to another drug.